When moving through the coverage area of a wireless access cellular network, mobile user terminals continuously scan the spectrum for pilot or reference signals (beacons) in order to determine which cell (base station) to camp on. In idle mode, this is referred to as cell reselection, while in active/dedicated mode, this is referred to as handover. The cell-specific list of surrounding cells that are considered for cell reselection or handover is called the neighbour cell list (NCL), which is stored in each base station and broadcast within the cell. The mobile user terminal receives and stores the NCL. The NCL contains the cells for which the mobile user terminal should send measurement reports (when certain criteria are met) to the base station currently serving the user terminal.
In case of multiple, cooperating wireless access cellular networks, each cell not only has an intra-network NCL, but also an inter-network NCL.
The optimisation of the NCLs is traditionally done with the aid of off-line planning tools, using path loss predictions and (off-line) optimisation algorithms. Currently, automated configuration and optimisation of intra-network NCLs and inter-network NCLs, based on e.g. actual measurement feedback from user terminals, observed mobility patterns, base station scans and handover statistics, are being investigated.
3GPP TS 36.300, V8.9.0, discloses an automatic neighbour relation (ANR) function to relieve an operator from the burden of manually managing neighbour relations. Such an ANR function resides in the eNode-B (eNB) of an LTE network and manages a conceptual neighbour relation table (NRT). A neighbour detection function is used to find new neighbours and to add them to the NRT, whereas a neighbour removal function removes outdated neighbours from the NRT. The eNB instructs a user terminal from a serving cell to look for neighbour cells of other networks by scanning all cells. The user terminal first reports the physical cell identifier (PCI) of the detected cells in the other network. When the eNB receives the reports from the user terminals containing the PCI's of the cells, the eNB instructs the user terminal, using the newly discovered cell as a parameter, to read the Cell Global Identifier (CGI) and further cell information from the neighbouring cells. The user terminal also reports this information to the serving cell. The eNB may then update the NRT using the information reported from the user terminals.